An enhanced rate of the high-Tc phase formation in the Bi–Ca–Sr–Cu–O superconductor by the two-step reaction and rapid heating

Abstract

An alternative synthetic approach was attempted for the fabrication of the Bi–Ca–Sr–Cu oxide superconductor. In this approach a mixed Sr–Ca–Cu oxide powder was first formed, and the resulting powder was subsequently reacted with Bi2O3. With this reaction scheme, problems associated with the low reactivity of CuO and SrCO3 can be partially removed by converting the mixed oxide/carbonate precursors to the reactive Sr–Ca–Cu compound. An enhanced rate of formation of the high-Tc (110 K) phase was observed in the two-step reaction, and this was explained in terms of the low activation free energy path for the formation of the high-Tc phase, which increased the decomposition rate of the remnant CuO. Under the condition of rapid heating, the formation of the high-Tc phase in the one-step reaction was expedited by the Cu-rich liquid phase. However, the liquid phase caused the formation of an insulating layer between the superconducting grains in spite of its catalytic activity in the high-Tc phase formation.